Inoue, U.S. Pat. No. 3,585,168 teaches a process for producing a high molecular weight polycarbonate by copolymerizing an epoxide, such as propylene oxide, ethylene oxide, styrene oxide, isobutylene oxide or epichlorohydrin with carbon dioxide. The process is carried out under carbon dioxide gas pressure in the presence of an organometallic compound catalyst. The polycarbonates formed by this process are made of substantially the same mole ratio of carbon dioxide and epoxide and have a molecular weight between 10,000 and 200,000.
U.S. Pat. No. 3,900,424 discloses a catalyst composition, and method of preparing said composition, for use in preparing copolymers of epoxy compounds with carbon dioxide. The catalyst composition comprises the reaction product of an organometallic compound, a co-catalyst component which is sulfur or a compound containing active hydrogen atoms and carbon dioxide.
U.S. Pat. No. 3,953,383 teaches a process for producing a copolymer of an epoxy compound with carbon dioxide by carrying out the polymerization reaction in the presence of a catalyst composition as described in U.S. Pat. No. 3,900,424. The copolymerization is carried out at a temperature within the range of from about 0.degree. C. to about 150.degree. C.
U.S. Pat. No. 3,248,415 discloses a process for copolymerizing carbon dioxide and a 1,2 epoxide, such as ethylene oxide, to yield polycarbonates of 700 to 5,000 molecular weight. The process is carried out in the presence of a small controlled concentration of an organic compound having at least 2, usually 2 to 4, active hydrogens such as a polyhydric alcohol at elevated temperature, superatmospheric pressure and preferably under conditions of base catalyst.
In Introduction to Polymer Chemistry by Raymond B. Seymour, (1971) at page 204 it is disclosed that "homopolymers with reactive end groups may be converted to block copolymers by reactions with the active end groups, such as hydroxyl, carboxyl, and amine groups. poly (ethylene oxides) with hydroxyl terminal groups may react with propylene oxide to product chains with different blocks of alkylene oxides."
In Textbook of polymer Science by Fred W. Billmeyer, Jr. at page 351, it is taught that block copolymers can be synthesized by producing "living" polymers by unterminated anionic polymerization. A second monomer can be added to the still active polymer, leading to a block copolymer uncontaminated with homopolymer and having blocks of accurately known and controlled length.